3D Digital Dentistry
Stereolithographic models in the planning of reconstructive surgery with bone grafts and sinus lifts.
Prototyping techniques make it possible to obtain anatomical replicas of the maxillae starting from computerized tomography. Stereolithographic models have been used for some time now together with surgical guides (Surgi-Guide™, Materialise n. v.) to optimize the implant position (1,2,3,4,5,6,7,8,9,10,11,12). We used the possibilities offered by these models to plan reconstructive surgery in a case requiring reconstruction of the bone with lateral grafts in the entire maxillary arch and bilateral sinus lifts. We designed and constructed three different surgical guides: one defining the dimensions of the iliac bone to be harvested, one to select the site of access to the maxillary sinuses and trace its perimeter and, finally, a guide for the preparation and positioning of the grafts.
CT showed bone defects in thickness and in height variously combined and widespread throughout the dental arch, corresponding to Cawood-Howell classes IV and V (13). In the posterior areas there were also bilateral sub-sinus defects 1 to 3 mm high (classes: D Jensen, SA 4 Misch) (14,15) (Fig.1,2).
Using thermoplastic resin on the stereolithographic model (Fig.3) we simulated the position of the grafts, modeling seven blocks of resin (Fig.4) attempting to achieve maximum fit with both the receiving bed and between one block and another (16,17,18,19).
Each block was numbered and we then constructed a bar equal to the sum of the individual blocks (Fig.5) to establish the size of the bone to be harvested.
For the sinus grafts (20) we designed a template (Fig.6) to quickly identify the most suitable area for osteotomy access to the maxillary sinuses.
The operation was performed under general anesthetic and consisted of three stages: in the first stage we removed the bone from the medial face of the iliac crest (21) (Fig.7), taking the amount of cortical-spongy bone indicated by the bar of resin plus a certain amount of spongy bone for the sinus lifts. The site of the harvest was then immediately sutured, drained and protected.
In the second stage, the maxilla was skeletized to the sinus lifts and the seven bone grafts were fixed in place. The template for the sinus lifts positioned on the bone (Fig.8, 9) guided the osteotomy for access to the sinuses (Fig.10),
Meanwhile, another surgeon cut the iliac bone into numbered blocks, using the resin models as fac similes (Fig.12).
After preparing the receiving bed (22), the grafts were positioned, attempting to obtain maximum adaptation with the bed and also between one graft and another (Fig.13,14).
The bone blocks were held in place with a compression clamp and fixed with osteosynthesis microscrews (Osteomed) (Fig.15).
Four months later, CT performed with a scanning prosthesis (Fig.16) showed complete integration of the grafts. It was therefore possible to carry out computer-aided implant site planning and construct a bone-supported Surgi-Guide™ based on the CT images.
Four months after the reconstruction operation all the grafts were well integrated and there was no inflammatory reaction after the sinus graft implantation. Four months after insertion of the implants they were all osteointegrated in accordance with Albrektsson & Zarb criteria (23).
The excellent adaptation between the parts and the absolute immobility facilitated revascularization of the grafts, favoring the take and the integration in the receiving site.
Planning the surgery with the stereolithographic (STL) models allows considerable precision in adapting the grafts to the receiving site and drastically reduces operating times. The guide for harvesting bone from the iliac crest allowing specific removal permits immediate closing of the access route, reducing the trauma and the risks of infection in this site.
The template for the sinus lifts allows more precise location of the osteotomy sites so that the caudal osteotomy is positioned a few millimeters higher than the sinus floor, favoring retention of the graft material. The size of the fenestrations are also in relation to the lateral nasal wall, considering any presence of Underwood’s transverse septi and ovals are traced to eliminate bone ridges.
Surgical planning on a STL model increases the accuracy and reduces operating time.
Marco Rinaldi, M.D., D.D.S., private practice Bologna, Italy.
via Marconi 45
Tel.: 051 233.600
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- Case: STL models in reconstructive surgery with bone grafts and sinus lifts.
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